Spark plug and method of making the same



Sept. 30, 1952 H. A. BRINSON ET AL v SPARK PLUG AND METHOD OF MAKING THESAME INVENTORS.

via/2%? 1 2% m l mui l/mg Filed Ndv. r 27, 1946 ATTORNEY Patented Sept.30, 1952 SPARK PLUG AND METHOD OF MAKING THE SAME Harry A. Brinson andEmbry D. Faatz, Sidney, N. Y., assignors to Bendix Aviation Corporation,New York, N. Y., a corporation of Delaware Application November 27,1946, Serial No. 712,636

This invention relates generally to spark plugs for internal combustionengines, and more particularly to a center electrode assembly that isadapted to be assembled as a unit in said spark plugs.

One of the objects of the present invention is to provide a novellyconstructed center electrode assembly for a spark plug.

Another object of the invention is to provide "a novel center electrodeassembly so constructed that the transfer of heat from the centerelectrode to the surrounding insulator is facilitated.

Another object is to provide a novel center electrode assembly which isso constructed that the leakage of gases through the bore of theinsulation surrounding the center electrode is substantially eliminated.

A further object is to provide a novel method of constructing the centerelectrode assembly of a spark plug.

A still further object is to provide a novel method of mounting a centerelectrode in the bore of an insulator whereby said bore is sub,-stantially filled by said electrode, thus providing a good contact ofhigh heat conductivity between said electrode and insulator.

Theabove and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameI is read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawing is for the purpose ofillustration only and is not intended to define the 9 Claims. (01.123-469) limits of the invention, reference for this latter purposebeing had primarily to the appended claims.

In the drawing, the single figure is an elevation view, partly insection and with parts broken away, showing a center electrode assemblyconstructed in accordance with the principles of this invention.

Referring to the drawing, the novel center electrode assembly indicatedgenerally at 5 is adapted for embodiment in spark plugs of the general.type disclosed in United States Patent No. 2,356,104, granted August 15,1944, to Tullio log nola. As shown, the center electrodev assemblylicomprises anfinsulator B molded or otherwise suitably' constructed ofsuitable ceramicor other'heatresisting material, and provided centrallythereof with a bore having three portions of diiferent lengths andincreasing in diameter from one end of said insulator to the oppositeend thereof. The shortest and smallest diameter bore portion 1 opensoutwardly through the lower end of insulator 6 and inwardly into thelower conical end of the longest intermediate bore portion 8 which issomewhat larger in diameter than bore portion 1 and opens outwardly intothe lower square end of the largest diameter bore portion 9 that issomewhat shorter than the bore portion 8 and opens outwardly through theupper end of insulator 6. The conical end of bore portion 8 and thesquare end of bore portion 9 form rests against the conical shoulder Illto hold said tip against endwise outward displacement from saidinsulator. Tip [2 is made of a corrosion resisting metal-which has ahigh melting point, such as platinum, for example. the intermediate boreportion 8 and extending for a substantial distance above the head 13 oftip I2 is a center electrode bar 14 of metal that softens at atemperature which will not appreciably affect the insulator 6 and thetip l2. Silver, which has a melting point of approximately 1760 F., hasbeen found suitable for this purpose when a platinum tip l2 which has amelting point of approximately 3200 F., and an insulator 5 of ceramic orlike material are used, Center electrode bar It is electricallyconnected to tip 12, and in order to insure good electrical contactbetween said bar and said tip a thin disc 15 of electrically conductivemetal that is fusible at a temperature which will not melt the bar l lis preferably disposed between the latter and tip 12.

A disc I5 of silver solder which has a melting point of approximately1240 F., and a remelting point of approximately 1340" F. which is abovenormal engine. operating temperature, has been found suitable for thispurpose when a silver bar [4 is used. U

Extending over the upper end of insulator 6 Disposed within andprojecting into the bore portion 9 is a terminal [G which is formed witha conical shank IT, a straight shank l8, and a socketed end I9 that issmaller in diameter than the diameter of said portion, the socket insaid end being provided with a conical upper wall. The bar l4 andterminal I8 are electrically connected by means of a conductor 20 whichis in the form of a wire made of any suitable resilient electricallyconductive material, such as, for example, molybdenum, and may be round,fiat, or half-round in transverse crossssection. Conductor 20 isprovided with a hooked upper end adapted to receive thereover the socket19 of terminal [5, a curved or bent intermediate portion, and a straightlower end which projects into a suitable opening 2| formed in the upperend of bar l4. Conductor 20 is mechanically and electrically secured tobar- I4 in any suitable manner, as by swedging the upper end of saidbar, .this operation being effected before the latter is placed ininsulator 6.

In making the center electrode assembly 5, the tip l2, the disc I5, andthe bar [4 with the conductor 20 secured thereto, are placed in theorder named in position through the upper end of insulator 6 with thehead l3 of said tip abutting the shoulder It, the disc resting on saidhead, .and the bar resting on said disc.

The annular space with the bore portions 8 and 9 around the conductor 29is then filled with a sealing material 22 which has a high melting pointand in its final form is a unitary rigid mass which has interlockingrelation with terminal [6 at the straight .-shank 18, as will appearhereafter, to thereby lead oxide and boro silicate lass is preferablyusedbecause of its insulating characteristics and its-coeefiicient ofexpansion. A satisfactory composition for the lead boro-silicate glasscontains 20 to 60% lead oxide and 80 to 40% of glass, the

of silicon dioxide, 12.3 parts of sodium tetraborate, 7.8 partsof boricacid, 2.2 parts of aluminum oxide, and .6 part of potassium carbonate.The described mixture of powdered glass and lead oxide will soften atapproximately 1400 R, a temperature below the melting points of the barM andtip l2, and above normal engine operating temperature. It will beunderstoodthat other types of sealing material may b employed which willbe plastic-like or pasty only when heated to a temperature above themaximum operating temperature of the spark-plug, but below anytemperature which might be detrimental to the parts of the assembly 5,i. e. to the insulator Band the parts installed in the bore thereof.

When the bore portion 5 is filled with a predetermined quantity of thesealing material 22 in finely divided powder form and said material issettled, such as by vibration of the assembly, tamping, or the like, theterminal I6 is then placed in the bore portion 9 with the socket I9thereof engaging the hooked end of conductor 20. vThe insulator 6 isthen heated in a suitable manner, as in a furnace or by directing one ormore flames from gas jets against the outer surface of said insulator,to a temperature between the melting point of disc l5 and the meltingpoint of .bar- [4, whereupon said disc is melted, said bar is softenedbut not melted, and the sealing. material 22'is rendered pasty orplastic. While insulator 6 is being heated, longitudinal compressionpressure. is applied by a suitable press or the like to the terminal l6,and when the disc i5 is melted, the bar i4 is softened, and the sealingmaterial 22 is rendered plastic, as described, the socket I9 of saidterminal is forced over the hooked end of the conductor 28 until saidend is properly seated within said socket and the head of the terminalis engaged with the upper end of insulator 6, whereupon longitudinalcompression pressure is applied by the terminal 16 to the plasticsealing material 22 causing it to hydraulically compress the softenedbar M in the longitudinal direction and thereby expand said barradiallywithin the bore portion 8 into contact with the surrounding wallof insulator 6. A total pressure of approximately 30 pounds uponterminal 13 has been found to be sufficient for this purpose when asilver bar I4 is used. When the plastic sealing material 22 iscompressed, as described, said material is alsov forced into the spacewithin and about the socket Iii and about the shank $8 of terminal Hi.

When the parts are assembled with contact established as illustrated anddescribed, the assembly is allowed to cool while maintaining sufficientpressure upon the terminal l6 until the sealing material 22 hassolidified. 1

With the hereinbefore described method of assembly, the insulator boreportion 8 is substantially filled by the bar 14 for at least a portionof the length thereof, thus providing good contact between said bar andthe wall of insulator 6 for good and rapid conduction of the heat fromthe bar to the insulator. All danger of the bar l4 melting and flowingdown the walls of the tip l2 to contaminate the latter is eliminated.The tip 12 and bar I4 are soldered together, therebyaiding inestablishing good electrical and heat conconducting contact between thesame. The escape of gases through the bore portion 9 isprevented by thesealing material 22 which also serves to hold the conductor 28 incontact with the terminal l6 and the parts in assembled relation.

The dimensions of the hooked end of conductor 20 are such that a firmcontact is established by the compression of said hook as the socket I9is forced thereover. The curved mid-section of the conductor 20 permitsthe latter to be compressed sufiiciently to insure proper seatingof thehooked end thereof insocket l9, and to be expanded or lengthened whenbar M is compressed. The conical wall in socket l9 provides four placesof contact for conductor 20, i. e. two upon the sides of said socket andtwo upon the sides of said wall. In order to insure good electricalcontact, between the conductor 20 and the terminal [6, the socket [9may, if desired. have solder therein which will melt when the assemblyis heated in the construction thereof.

There is thus provided a novel center electrode assembly wherein alongitudinally extending portion of the bore in the insulator is substantially filled by a solid portion of thecenter electrode, thusproviding a good contact between the center electrode and the insulatorfor rapid conduction of the heat from said center electrode to saidinsulator. There is also provided a novel method of assembling thecenter electrode in the insulator whereby filling of the bore-in said isulator by said center electrode is effected Without danger ofcontaminating the exposed tip thereof.

Although only a. single embodiment of the invention is illustrated inthe accompanying drawins and described in the foregoing specification,

' andscope of the invention, as will now bejapparent to those skilledin'the'art. For example, thejdisc "15 may be eliminated andproperelectrical contact-between the up-12 m thebarll may be establishedwhen theljlatter is compressed during the assembling'operation. Foradefinition of the limits "of the invention, reference is had primarilyto the appended claims. .\What is claimed is;

1; A center electrode assembly for a spark plug comprising an insulatorhaving a bore therethrough, a metallic electrode tip projecting fromsaid bore, a metallic electrode bar which has been compressed withinsaid bore in a direction towards said tip and thereby expanded radiallyinto contact with the insulator wall surrounding said bore, and meansfused in said bore between said tip and said bar and forming anelectrically conductive connection therebetween.

2. A center electrode assembly comprising an insulator having a boretherethrough, portions of said bore being of different diametersproviding a shoulder therebetween, a metallic electrode tip projectingthrough the smaller portion of said bore and having a laterallyprojecting portion disposed within the larger portion of said bore andenga ed with said shoulder, a metallic electrode bar disposed within thelarger portion of sa d bore and which has been compressed therein in adirection towards said tip and thereby expanding radiallv into contactwith the insulator wall surrounding said larger bore portion, 7

said bore being of different diameters providing 1 a shouldertherebetween, a platinum electrode tip proiectin through the smallerportion of said bore and having a laterally proiecting portion dis osedwithin the lar er portion of said bore and en a ed with said shoulder, asilver electrode bar disposed within the larger portion of said adirection towards said tip and thereby expanded radially into contactwith the insulator wall surro nding said larger bore portion, and asilver alloy disc fused in the larger bore portion and bore and whichhas been compressed therein in cally and electrically secured-togetheras a single 5. The method of making-a center electrode assembly havingan insulator with a central bore,

which comprises placing a metallic'electrode tip,

'ametallic disc and a metallic electrodebar in said bore'in the ordernamed and in abutting relation with the tip projecting in part from-oneend of the bore and the free end of the bar spaced inwardly from theopposite end-of 'saidbore, said bar having a melting point below themelting point of said tip and said disc having a melting point below themelting point of said bar, filling a portion of the space within thebore above the bar with a mixture of finely divided fusible materials ofwhich one component has a melting point below the melting point of saidbar, heating said insulator, tip, disc, bar, and mixture to atemperature below the melting temperature of said bar at which said barbecomes soft, said disc becomes molten andsaid mixture becomes plastic,applying pressure to said mixture whilst in the plastic state in adirection towards said bar whereby the latter whilst in the softenedstate is compressed by said mixture in a longitudinal direction andexpanded radially into contact with the surrounding wall of saidinsulator,

and then cooling the entire assembly.

6. A spark plug center electrode including an insulator tube having asmaller internal shoulder toward one end and a larger internal shoulderbetween the first shoulder and the other end, a spark electrode abuttingthe smaller shoulder and projecting from the end, a bar soldered to saidspark electrode and compressed within the tube between the shoulders, ahooked wire set in the bar and projecting past the second shouldertoward the other end of the tube, in-

sulation under pressure against the bar and about the wire, and a capelectrode sealing the other end of the tube having a socket receivingthe hooked end of the wire in compressed insulation.

7. A spark plug center electrode including an insulator tube having asmaller internal shoulder toward one end and a larger internal shoulderbetween the first shoulder and the other end,

a spark electrode abutting the smaller shoulder and projecting from theend, a bar connected to said spark electrode and compressedwithin thetube between the shoulders, a flexible connector set in the bar andprojecting past the second shoulder toward the other end of the b tweenthe bar and the tin and forming an electricallv conductive connectionbetween said bar and said tip.

4. The method of making a center electrode assembly having an insulatorwith a central bore,

which includes the steps of placing a metallic electrode tip, a metallicdisc, and a metallicelectrode bar in said bore in the order named and inabutting relation and with the tip projecting in part from said bore,said tip, disc and bar having different melting points, heating saidinsulator, tip, disc and bar to a temperature at which said bar becomessoft without melting and said disc becomes molten, applying pressureupon the exposed end of said bar whilefit is in softened state to causethe latter to expand radially into contact with the surrounding wallofsaid insulator, and then cooling the assembly whereby the compressed barand the tip are mechanitube, insulation under pressure against the barand about the flexible connector, and a cap electrode at the other endof the tube having a socket receiving the hooked end of the wire incompressed insulation.

8. A center electrode assembly for a spark plug comprising an insulatorhaving a bore therein with an internal cone-like seat adjacent one endthereof, an electrode tip having a portion projecting from said bore anda head portion engaging said seat and substantially filling the adjacentportion of said bore, and a solid section -of metal expanded intoengagement with the walls of said bore and having the end thereof bondedto said head portion, such as by soldering.

9. A center electrode assembly for a spark plug comprising an insulatorhaving a bore therein with an internal cone-like seat adjacent one endthereof, an electrode tip having a portion adjacent portion of saidbore, a solid section of 7 metal; expanded into: engagement with thewalls 7 BEIFEBJ'JN(3E8 CITED of said bore and having the end thereofbonded r n references are of record the to"saidi.-head portion, such asby soldering, a me of this. patent; wire connector having a. bend at oneend and the" other end thereof embedded in said metal 5 v UNITED STATESPATENTS 7 section, :a terminal. having. a recess for receiving NumberName Datethe bend at the end of said wire and an en- ,293,381 CaringtonAug. 18,1941? larged portion in said bore, and a solid mass of 2,3 0,287Smith Oct. 10,1944 electrically non-conductive sealing material en- 2,40,917 Corbin May 28, 1946 eompassing said enlarged portion and fillingthe 10 2, 06,966 Pfeil p 3, 1 bore around said wire. v 2,416,107 Litton.Feb. 18, 1947 v HARRY A. BRINSON. I FOREIGN PATENTS D. Number CountryDate 7 t a 15 559 805 Grea Britain Mar: 1944

